Hi

I would be incredibly grateful for any advice. I am based in Dubai and finding a good plumber is hard...

Our house has a large fresh water tank filled by mains under the driveway. A pump at ground level pulls cold water from the tank and pressurises the cold water supply to the house.

We frequently loose most of the pressure (especially upstairs). If I run a tap upstairs for a period (20 - 30 minutes ) the pressure will come back. Everything works great for one or two days and then the pressure goes again.

I am assuming that air is getting into the system? Any advice on how to diagnose this or fixes that could be applied be great fully received.

The plumber the landlord sent initially tried to tell me the pathetic dribble of water we get was normal. Long story short I need to be pretty clear on what to tell him to do otherwise this will never get fixed!

Let me know if I can supply any additional info !

Generally speaking, there is no way for air to enter your closed, pressurized, plumbing system. And if it did - like during pipe replacement - it would escape first time you run your faucet. I would look at the pump as pump is responsible for pressurizing the system and to hold the pressure within the pre-set high/low limits. It seems to me your low pressure limits are not set properly

Lets see what other Experts have to say

Milo

Because things are often done differently at different places we have to be very clear about how and why things are done.

First tell us why this is being done this way, if you know.

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Our house has a large fresh water tank filled by mains under the driveway

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I assume that you mean that the tank is under the drive way not the mains.

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A pump at ground level pulls cold water from the tank and pressurises the cold water supply to the house.

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Are you certain about that statement. Where is the pump? Is it between the mains and the tank or is it between the tank and the house? That question is ask in the terms of piping, not physical location.

What kind of controls are on the pump? There should be a pressure switch to tell the pump when to run and a pressure gauge to tell you what is going on.

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If I run a tap upstairs for a period (20 - 30 minutes ) the pressure will come back.

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Does the same happen if you run a tap downstairs?

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I am assuming that air is getting into the system?

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In a pressurized system you don't have air in the system. If you do get air in the system, because air is lighter than water, it comes out as soon as you open a tap.

So tell us how things are done as best you know and why. Keep what you say short and simple. I am a simpleton, you would be surprised how many ways I can interrupt what you say.

I have preconceived concepts about how things are done and why. To express them now would only contaminate the conversation.

So confirm that the tank is under the driveway. How large is the tank? Tell us the timing and what the circumstance are when the low pressure occurs. Does opening a downstairs tap restore pressure like the upstairs tap. When you experience a pressure loss what is the pump doing, is it running? Do you have a pressure gauge and what is its reading?

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The plumber the landlord sent initially tried to tell me the pathetic dribble of water we get was normal

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Perhaps because you are on the other side of the world everything is upside down but statements like that are universal. When we get to Mars there will probably be someone or something there saying "Oh, that's normal".

Hi

Good questions! I will clarify as best as I can tonight and gather additional info in the morning. Posting what I can now I'm case additional questions are triggered.

Milo I see what you mean re the low pressure limit. However, after running the tap for an extended period I can then shut it off. When I come back and open that tap or the shower I straight away get high pressure. This lasts for anything from a few days to a few hours. I think it used to last a lot longer. Does that rule out bad set points for the pump?

hkstroud

The tank is under the drive. It is very large. Large enough to climb into. During a previous maintenance issue (failed non return valve?) the plumber borrowed some old clothes from me and jumped into the tank. Maybe a 1 m shaft and 2 m deep tank. The tank has a simple cast iron or steel man way cover filled with block work on top. It's in no way pressurised. The tank is fed by mains water.

The pump is between the tank and the house. There are in fact two pumps. Number one pump operates on demand (when a tap is opened) so I guess it's pressure operated (will confirm in the morning, provide readings etc.). Number 2 pump drives the irrigation system and operates on a timer.

It's also worth mentioning there are lots of high points in the pipework. The pipework goes upstairs and then reaches the bathrooms via a false ceiling. In other words the pipe has to come back down before it reaches every single tap upstairs. A couple of small hot water tanks are also tucked away in the false ceilings.

Good question re

1) running a downstairs tap. I will try next time the water pressure fails.
2) what does the pump do when the pressure is low. Don't know I will check. Don't think it activates to try and maintain system pressure.

Well I'm glad I didn't try to second guess the way the system works. Frankly I expected you to come back saying you had pressurized tank fed from the mains. Essentially a well system fed by the mains instead of a well.


So you have a holding tank fed by the mains. That tank cannot be a pressure tank not can it be air tight. Therefore, water into the tank must be controlled by some kind of float control.

Next time you lose pressure and volume in the house, run outside and look in the tank. Is there water in the tank and is it at or above the piping to the pump? Could the water level in the tank have temporarily dropped below the level of the pump line?

If you have sufficient water in the tank, is the pump motor running?
If the pump motor is running feel the connecting pipes. Do you feel or hear any water movement. The pump motor could be running but the actual pump might not be turning. Also, the pump motor could be running and actually turning the pump but not pumping any water.

You said you have a separate pump for the irrigation system. Is it running? The house pressure pump and the irrigation pump are most likely on the same pipe from the tank. If the irrigation pump is running could it be taking all the water from the tank?

If the irrigation pump is not running, turn it on and see if it works as it should.

You could have a break or leak in the piping from the tank to the house pump. If air is drawn in, either from a break in the piping or from a low water level in the holding tank, a temporary pump failure could occur. It is a water pump, not an air pump. With a volume of air in the pump chamber, the impeller would not be able to push the air out, therefore not be able to pull more water in.

From the symptoms you have describe I think this is most likely what is happening. When you leave a tap open, there by reducing the pressure on the discharge side of the pump, the pump is gradually able to move the air out and begin pumping water again.
Temporarily turning the irrigation pump on might restore the house pump and pressure quickly. If there are no check valves involved, the irrigation pump would pull water, therefore any trapped air, from the house pump.

Be a good idea to feel and listen to the pump and piping when everything is working so you will know if there is any difference when it is not.

Please keep us posted, this will be an interesting one.

Thanks. I will definitely investigate further and feedback.<br><br>I can confirm the water level in tank is way below the level of the pump.&nbsp;The tank is below ground and the pump is at ground level. <br><br>Wondering if I have missed something as I cannot understand how the pump primes itself?

No the question is;
Is the water level in the tank below where the pipe to the pump is connected to the tank?

In other words can the pump be sucking in air?

Logic would say that the tank should be completely full unless there is a problem with the float mechanism, or there is a lack of supply from the mains, or you have pumped all the water out of the tank and it is in the process of refilling. Granted if you run the pump long enough it will pull out all the water in the tank, plus what came in from the mains while you were pumping. If that wasn't the case you wouldn't need the tank. However, that should be an extended time. More than even the most demanding times of normal use.


Edit
It is quite likely that the pipe from the pump comes in from the side of the tank. Then turns down and goes down to the bottom or close to the bottom of the tank. If plumbed that way you wouldn't have to worry about a leak around where the pipe comes in. If that is the way the pipe is run, the question would be is the water level higher than the end of the pipe that goes to the bottom of the tank?

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Originally Posted by hkstroud

No the question is;
Is the water level in the tank below where the pipe to the pump is connected to the tank?

In other words can the pump be sucking in air?

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Had a good poke around yesterday. After I shoo'do away the geckos and camel spiders I found the following:

1) When running the pump is noisy. It sounds like air is going through. How much I don't know. The previous problem we had was when something failed in the main tank and water flowed back so the pipework has been messed with.
2) Very hard for me to check the tank connections. The hatch is too heavy for an individual to lift (took 3 of us last time ) and I don't have the tools. It is possible that the tank gets drained down but none of my neighbours are reporting similar problems (houses are identical ). Things can be erratic in Dubai so it would not surprise me though.
3) There is no pressure gauge. The house pump is controlled on discharge pressure by a grundfos controller. Fixed operating set pressure of 1.5bar. Both pumps are by Grundfos.
4) Most pipework is buried in the sand and hard to trace. The discharge from the house pump splits in two. One line has a doohickey with a knob of some sort in it. I am guessing to regulate the flow. Perhaps the split is between upstairs and downstairs?
5) the inlet to both pumps has a stud in casing. I am guessing this is a to bleed air or prime the pump. The Stud in the house pump has been wrapped in lots and lots of ptfe tape.

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The house pump is controlled on discharge pressure by a grundfos controller.

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Grundfos controller would be another name for a built in pressure switch.

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3) There is no pressure gauge.

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Would be helpful if there was one but you already know that you have lost pressure.

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One line has a doohickey with a knob of some sort in it. I am guessing to regulate the flow.

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Are you sure it's a dohickey? Could it be a thingamajig or maybe a whatchamacallit?
Show a picture.

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When running the pump is noisy

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It is hard to quantify what you mean by noisy. Generally you should not hear anything on a Grundfos except the hum of the motor. And that should ot be very loud. How does the sound of the house pump compare to he sound of the irrigation pump?

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the inlet to both pumps has a stud in casing

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By stud I assume you mean plug. Yes that would be to prime the pump.

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The Stud in the house pump has been wrapped in lots and lots of ptfe tape.

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Suggest removing the tape and see why its there. If it is the source of an air leak, that would cause the pump to loose its prime.

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It is possible that the tank gets drained down

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Running the irrigation pump when you have a pressure loss in the house would eliminate that possibility.

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